From the top of my mind (and my HDD), in no particular order:
Cube (this movie depicts one of the most carefully and elaborated atmospheres ever created in a movie);
Fear and Loathing in Las Vegas (I don't have much to say on this one, but it sure is quite educating, in many senses);
Tetsuo / The Ironman (everybody must watch this… at least once);
Eraserhead (probably the scariest movie I ever saw);
Interstate 60 (while looking a bit casual, this movie actually is incredibly… hmm… wise);
Indiana Jones and the Temple of Doom (was one of my favourite movies when I was a kid);
The Thing (a rather underrated movie, though really impressive in almost every aspect);
The Matrix trilogy + Animatrix (not very original in its idea and symbolism, but very good nonetheless);
Monty Python and the Holy Grail (probably the funniest movie I ever saw);
Once Upon a Time in America (a movie that is spectacular in one aspect: you will notice new details each time you watch it, a very rare quality);
Terminator 2 (thanks for reminding, atro city; this is one damn good action movie).
As for the anime, if it even counts:
Neon Genesis Evangelion /
The End of Evangelion (I don't think a simple description would do it any justice);
Princess Mononoke (touching and beautiful, though it is a common description for any of Miyazaki's movies);
Spring and Chaos ("a unique biographical sketch of the life of the great modern Japanese poet Kenji Miyazawa");
Dead Leaves (best action movie ever!);
Azumanga Daioh (incredibly funny);
Now and Then, Here and There (I almost wept over the last two episodes; very emotionally intense);
Excel Saga (another totally hilarious anime, a must for everyone).
[Another space intentionally left blank].
Tiger Robocop !!!! XDDDD
